Travel in space for a relatively long duration imposes a unique set of requirements for the bathing of crew members. In addition to the primary reason for bathing which is to satisfy the physiological, psychological and social needs of the crew throughout the duration of duty in a space vehicle, the cleansing agent utilized in bathing must also be compatible with any water reclamation system used to purify and recycle the water used for bathing.
Initial considerations in developing a suitable whole body cleansing agent for use on a space station involve the recognition of the criticality of using a minimum quantity of resources. Thus, bathing is performed using a minimum quantity of water and employing a single cleansing agent suitable for use on the skin as well as the hair. Low water usage of about 4 liters per shower is a key objective.
Since the system uses deionized water, particular attention must be paid to rinseability. For example, conventional solid soaps become very difficult to rinse in deionized water. Also, to simplify housecleaning, the cleansing agent should not leave a film on surfaces of the shower. Since unnecessary weight should desirably be eliminated, a concentrated form of cleansing agent is also desired.
Water reclamation systems used on space stations generally require that the water being reclaimed is low foaming since such equipment will not generally function properly with high foaming solutions. On the other hand, cleansing agent consumption increases drastically if the cleansing agent does not foam, and one's perception of cleanliness is low if foam levels are low.
Water reclamation can be complicated by the presence of unnecessary ingredients typically found in commercial liquid shampoos for providing a consumer-attractive form, fragrance and appearance. Water reclamation would be simplified if the cleansing agent contained 4 or fewer ingredients.
It is known that water does not drip or run off the body during a microgravity shower, making it more difficult to rinse the cleansing agent, especially from the hair. Microgravity conditions also require special attention to potential eye irritation by the cleansing agent because it is more difficult to rinse the cleansing agent from the eyes under microgravity conditions. In addition, high viscosity, concentrated cleansing agents are generally more irritating to the eyes and are more difficult to remove therefrom by blinking.
Because the whole body cleansing agent is applied in microgravity conditions, it should be very viscous to facilitate dispensing and application. The cleansing agent should lather effectively to a high- volume, stable and thick foam structure. Inadequate foaming leads to excessive use and does not provide a feeling of cleanliness thereafter. Foaming also facilitates spreading of the lather, efficient soil removal, and rinsing of the cleansing agent from the body.
On the other hand, as earlier stated, a water reclamation unit will not function properly with high foaming solutions.
In addition to the foregoing special considerations in microgravity, low-water-consumption considerations, the cleansing agent must perform the usual functions of soap and shampoo, providing a good feel on the skin and hands, clean and fresh-smelling hair, good hair luster, ease of combing wet hair, speed of drying of the hair, ease of combing and setting of dry hair, good control of dandruff, good odor of the cleansing agent, good residual odor on the body following use of the cleansing agent, must be non-toxic, non-irritating to the skin, non-irritating to the eyes, nonallergenic, and must not cause dermatitis or skin defatting.
As far as applicant is aware, no such cleansing agent has heretofore been available which meets the criteria for a suitable whole body cleansing agent for use in a shower system aboard a space station.